76 The Vertebrate Organ Systems 



cessive evaporation of water from the body. Water, of course, is 

 absolutely essential for all bodily processes ; so its conservation is of 

 utmost value. The absorption of excessive water into the body could 

 also be harmful. Again the skin plays an important role, for the 

 oily surface is an effective waterproof covering. For aquatic verte- 

 brates this is an especially important function. 



To many animals, the integument plays an important role due 

 to its color. Often it is colored in such a manner as to make the animal 

 nearly invisible when in its proper habitat. For others such as the 

 skunk, conspicuous colorings serve as warning signals, thus protecting 

 their owners. 



For the frog, the slippery skin surface is often of aid in escaping 

 from would-be captors. The slippery surface is nearly impossible to 

 retain. Other animals such as the porcupine are well-equipped with 

 quills, while the armadillo has a heavy scalelike surface. 



2. Heat Regulation. All metabolic activities of any animal 

 result in the production of heat. This is distributed through the body 

 by means of the circulatory system, and then is lost through the lungs, 

 feces, urine, or skin. It is probable that nearly nine-tenths of this 

 loss occurs through the skin. Thus it is clear that heat regulation is 

 an extremely important function of the integumentary system, one 

 which is of greatest significance among those vertebrates that main- 

 tain a relatively constant body temperature (the homoiothermic animals). 



When environmental temperatures are the same or lower than 

 that of the body, it is necessary for the homoiothermic animal to con- 

 serve heat. In the deeper layers of skin, fat, an effective insulator, 

 is stored. The greater the amount of fat, the greater the insulation. 

 The aquatic mammals, such as the whale, have tremendous layers of 

 blubber which serve to hold the heat of the body and make it possible 

 for these mammals to live in icy water. Animals which do not main- 

 tain a constant temperature (the poikilothermic animals) do not have 

 these heavy storage layers of fat within their skin. 



The oil on the surface of the skin probably also is helpful in 

 retaining body heat. The hair of mammals and the feathers of birds 

 likewise are excellent insulating materials. Air is trapped within the 

 layers of feathers or hair and forms a warm, dead air .space. The 

 thickness of this layer can be adjusted by fluffing of feathers or the 

 raising of the hairs. Some mammals grow heavier coats of hair during 

 the winter months. Due to the reduction of his hair cover, man must 

 rely upon clothing to accomplish this heat conservation. 



